Method of coating an emissive element

Abstract

An electrode for a plasma arc torch and method of fabricating the same are disclosed, wherein the electrode comprises a metallic holder defining a cavity in a forward end. An emissive element and separator assembly is positioned in the cavity. The emissive element has a layer of relatively non-emissive material on the outer surface thereof, which is preferably applied by heating the emissive element to a high temperature such that the emissive element becomes reactive, and spraying the relatively non-emissive material on the emissive element. The coated emissive element is positioned in the separator and the assembly is heated such that the relatively non-emissive material forms a strong bond between with the separator. The superior bonds between the emissive element and separator formed according to the present invention extend the life span of the electrode.

That which is claimed:  
     
       1. A method of coating an emissive element for use in a plasma arc torch, the emissive element having an outer surface, the method comprising: 
       heating the emissive element such that at least a portion of the outer surface of the emissive element becomes reactive;  
       applying a relatively non-emissive material to the heated and reactive outer surface of the emissive element;  
       allowing the relatively non-emissive material to melt against the outer surface of the emissive element; and  
       allowing the emissive element and relatively non-emissive material coated thereon to cool so that the relatively non-emissive material and the outer surface of the emissive element are securely bonded together.  
     
     
       2. A method according to  claim 1 , wherein the heating step includes heating the emissive element to at least 1400° F. 
     
     
       3. A method according to  claim 1 , wherein the heating step includes heating the emissive element such that substantially all of the outer surface of the emissive element becomes reactive. 
     
     
       4. A method according to  claim 1 , wherein the applying step comprises spraying a material on substantially all of the outer surface of the emissive element, the material being selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, nickel, aluminum, and alloys thereof. 
     
     
       5. A method according to  claim 4 , wherein the applying step comprises spraying the material in a powdered form. 
     
     
       6. A method according to  claim 4 , wherein the applying step includes spraying the material from a spray torch during the heating step. 
     
     
       7. A method according to  claim 4 , wherein the applying step includes applying the relatively non-emissive material having a thickness of about 0.002-0.010 inches to the outer surface of the emissive element. 
     
     
       8. A method according to  claim 1 , wherein the melting step occurs substantially concurrently with the applying step. 
     
     
       9. A method of forming an emissive element for use in a plasma arc torch, the emissive element having an outer surface, the method comprising: 
       heating the emissive element to about 4000° F. such that the outer surface of the emissive element becomes reactive;  
       spraying a relatively non-emissive material on the heated and reactive outer surface of the emissive element to form a layer having a thickness of at least 0.002 inches;  
       allowing the relatively non-emissive material to melt against the heated and reactive outer surface of the emissive element upon contact therewith; and  
       allowing the emissive element and relatively non-emissive material coated thereon to cool so that the relatively non-emissive material and the outer surface of the emissive element are securely bonded together.  
     
     
       10. A method according to  claim 9 , wherein the spraying step includes spraying a material selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, nickel, aluminum, and alloys thereof. 
     
     
       11. A method of forming an electrode for use in a plasma arc torch, the method comprising: 
       heating an emissive element having an outer surface such that at least a portion of the outer surface of the emissive element becomes reactive;  
       applying a relatively non-emissive material to the heated and reactive outer surface of the emissive element;  
       allowing the relatively non-emissive material to melt against the outer surface of the emissive element and be securely bonded thereto;  
       positioning the emissive element in a cavity defined by a relatively non-emissive separator such that the cavity is substantially filled by the emissive element; and  
       bonding the emissive element to the relatively non-emissive separator.  
     
     
       12. A method according to  claim 11 , wherein the heating step includes heating the emissive element to at least 1400° F. 
     
     
       13. A method according to  claim 11 , wherein the heating step includes heating the emissive element such that substantially all of the outer surface of the emissive element becomes reactive. 
     
     
       14. A method according to  claim 11 , wherein the applying step comprises spraying a material on substantially all of the outer surface of the emissive element, the material being selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, nickel, aluminum, and alloys thereof. 
     
     
       15. A method according to  claim 14 , wherein the applying step comprises spraying the material in a powdered form. 
     
     
       16. A method according to  claim 14 , wherein the applying step includes spraying the material from a spray torch during the heating step. 
     
     
       17. A method according to  claim 14 , wherein the applying step includes applying the relatively non-emissive material having a thickness of about 0.002-0.010 inches to the outer surface of the emissive element. 
     
     
       18. A method according to  claim 11 , wherein the melting step occurs substantially concurrently with the applying step. 
     
     
       19. A method according to  claim 11 , wherein the bonding step includes heating the emissive element and separator such that the relatively non-emissive material and separator are securely bonded together. 
     
     
       20. A method according to  claim 19 , wherein the bonding step includes heating the relatively non-emissive material to the melting temperature thereof. 
     
     
       21. A method according to  claim 11 , wherein the positioning step includes positioning the emissive element in a cavity defined by a relatively non-emissive separator that is formed of a material selected from the group consisting of silver, gold, platinum, rhodium, iridium, palladium, nickel, aluminum, and alloys thereof. 
     
     
       22. A method according to  claim 11 , wherein the applying step includes applying a relatively non-emissive material that is substantially similar to the material forming the separator.